1. Field of the Invention
The present invention relates to an image processing device, an image processing method, a non-transitory computer readable medium storing an image processing program, and an inkjet recording device, and more particularly, to a technique for correcting streak unevenness caused by a defective nozzle of an inkjet head.
2. Description of the Related Art
In a single-pass-type inkjet printer (inkjet recording device), streak unevenness occurs in the transportation direction of a sheet due to a defective nozzle such as a non-discharging nozzle or a nozzle which discharges ink in an incorrect direction. In order to solve the problem, a technique is known which masks a defective nozzle and controls concentration in the vicinity of the defective nozzle to reduce the visibility of streaks.
As a method for controlling concentration in the vicinity of the defective nozzle, a technique is known which modulates a plurality of pixels in the vicinity of the defective nozzle. For example, JP2006-76086A discloses a technique which corrects a gradation value in the vicinity of a defective nozzle on the basis of the amount of correction that is reduced as the distance from the defective nozzle increases and controls a recording head such that a larger dot is recorded as the gradation value becomes larger.
In addition, as another method for controlling concentration in the vicinity of the defective nozzle, a technique is known which changes a dot size and fills a streak that occurs due to, for example, a curved discharge with dots to correct the streak.
For example, JP2006-130904A discloses a technique which, when the occurrence of a banding phenomenon is expected on the basis of the characteristic information of a head, converts image data such that the size of some or all of the dots related to the banding phenomenon is changed to a size different from the size of the dot when the occurrence of the banding phenomenon is not expected.
In addition, JP2006-182023A discloses a technique which changes a dot size on the basis of the discharge accuracy information of a head to generate printing data and performs printing on the basis of the generated print data.
JP2007-98937A discloses a technique which determines the generation rate of dots with a different size for each predetermined region of image data on the basis of acquired concentration unevenness information and converts the image data into N-values on the basis of the determined generation rate.